CN114460822A - Charging roller, process cartridge, and electrophotographic image forming apparatus - Google Patents

Abstract

The invention relates to a charging roller, a process cartridge, and an electrophotographic image forming apparatus. A charging roller comprising a conductive core shaft and a conductive layer as a surface layer, the conductive layer comprising a matrix containing a crosslinked product of a first rubber and domains dispersed in the matrix, the domains each containing a crosslinked product of a second rubber and conductive particles, the domains each having a volume resistivity smaller than that of the matrix, and 50% by number or more of all the domains in a cubic sample having a side length of 20.0 μm satisfying a specific condition when the cubic sample is sampled from an outer surface of the conductive layer to a depth of 20.0 μm.

Description

Charging roller, process cartridge, and electrophotographic image forming apparatus

Technical Field

The present disclosure is directed to a charging roller, a process cartridge, and an electrophotographic image forming apparatus.

Background

In an electrophotographic image forming apparatus employing a contact charging system, a charging roller for charging a surface of an electrophotographic photosensitive member is disposed adjacent to the electrophotographic photosensitive member.

The charging roller includes a conductive substrate and a conductive layer on the substrate. Further, in the electrophotographic image forming apparatus, a voltage is applied between the conductive substrate of the charging roller and the electrophotographic photosensitive member, and is discharged from the surface of the conductive layer of the charging roller facing the electrophotographic photosensitive member (hereinafter also referred to as "outer surface") toward the electrophotographic photosensitive member. Thus, the surface of the electrophotographic photosensitive member facing the charging roller is charged.

In japanese patent application laid-open No. 2002-: a polymer continuous phase formed from an ionically conductive rubber material; and a polymer particle phase formed of an electronically conductive rubber material.

According to the study of the inventors, when the charging roller according to japanese patent application laid-open No.2002-3651 is used to form an electrophotographic image under a low-temperature and low-humidity environment such as a temperature of 15 ℃ and a relative humidity of 10%, stripes (hereinafter also referred to as "horizontal stripes") extending in a direction perpendicular to the circumferential direction of the charging roller are formed in the electrophotographic image in some cases.

Disclosure of Invention

At least one aspect of the present disclosure is directed to providing a charging roller useful for stably forming high-quality electrophotographic images under various environments. Further, another aspect of the present disclosure is directed to providing a process cartridge which is useful for stably providing an electrophotographic image of high quality. Further, still another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus capable of stably forming an electrophotographic image of high quality. According to an aspect of the present disclosure, there is provided a charging roller including: a conductive mandrel; and a conductive layer as a surface layer, the conductive layer including a matrix containing a crosslinked product of a first rubber and domains dispersed in the matrix, the domains each containing a crosslinked product of a second rubber and conductive particles, the domains each having a volume resistivity smaller than that of the matrix, wherein when a cubic sample having a side of the conductive layer of 20.0 μm is sampled from an outer surface of the conductive layer to a depth of 20.0 μm, 50% by number or more of all the domains in the cubic sample satisfy the following condition:

< Condition >

Assuming that the domain to be evaluated in the cubic sample is enveloped by an enveloping cuboid having two surfaces each perpendicular to a line segment L passing through at least one arbitrary point in the domain to be evaluated and perpendicular to the surface of the mandrel, "X" is longer than "Y" and "Z", where "X" is the length of the enveloping cuboid in the X-axis direction, "Y" is its length in the Y-axis direction, and "Z" is its length in the Z-axis direction, and a line segment S perpendicular to the line segment L and parallel to the X-axis can be drawn.

According to another aspect of the present disclosure, there is provided a process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, the process cartridge comprising: an electrophotographic photosensitive member; and the above-described charging roller configured to be capable of charging the electrophotographic photosensitive member.

According to a further aspect of the present disclosure, there is provided an electrophotographic image forming apparatus including: an electrophotographic photosensitive member; and the above-described charging roller configured to be capable of charging the electrophotographic photosensitive member.

Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

Fig. 1 is a perspective view of a charging roller according to an aspect of the present disclosure.

Fig. 2A is a schematic diagram of a cross-section of a conductive layer in a length direction thereof according to an aspect of the present disclosure.

Fig. 2B is a schematic view for explaining a state of a domain existing in a surface region from an outer surface of a conductive layer according to an aspect of the present disclosure to a depth of 20 μm.

Fig. 3 is an illustrative diagram of one domain in a conductive layer in accordance with an aspect of the present disclosure.

Fig. 4 is an explanatory diagram of domains that do not satisfy the conditions according to the present disclosure.

Fig. 5 is an explanatory diagram showing an angle of a direction in which the domain extends according to the present disclosure.

Fig. 6 is a diagram for explaining a schematic configuration of a crosshead extrusion apparatus.

Fig. 7 is a histogram summarizing the angular distribution of inferior angles.

Fig. 8 is a sectional view of a process cartridge according to one embodiment of the present disclosure.

Fig. 9 is a sectional view of an electrophotographic image forming apparatus according to one embodiment of the present disclosure.

Detailed Description

When an electrophotographic image is formed under a low-temperature and low-humidity environment using the charging member according to japanese patent application laid-open No. 2002-.

The charging member rotates in a state of abutting on the electrophotographic photosensitive member, and therefore an electric charge may be generated on the surface of a portion of the charging member abutting on the electrophotographic photosensitive member (hereinafter also referred to as "nip portion") by friction of the charging member with the electrophotographic photosensitive member. In order for the surface of the charging member to exhibit a function of releasing charges to the electrophotographic photosensitive member, a predetermined conductivity is imparted to the surface by an ionic conductive agent or an electronic conductive agent. Therefore, triboelectric charges generated on the surface of the charging member by friction with the electrophotographic photosensitive member are diffused, but the directionality of the diffusion is not controlled, and thus a portion where the electric charges are locally high may exist in the region of the conductive layer of the charging member ranging from the nip portion surface of the conductive layer to the mandrel of the charging member. Then, the portion where the electric charge is locally high causes the discharging unevenness of the charging member. Then, such discharge unevenness may cause potential unevenness on the surface of the electrophotographic photosensitive member. In view of the above, the present inventors have studied the configuration of a charging member capable of controlling the direction in which frictional charges generated on the surface of the charging member diffuse, with a view to preventing a portion where charges locally stay from occurring in an elastic layer of the charging member. As a result, the present inventors have found that the following charging member can control the direction in which triboelectric charges generated on the surface thereof diffuse.

That is, the charging member according to an aspect of the present disclosure includes a conductive mandrel and a conductive layer serving as a surface layer. The conductive layer includes a matrix including a first rubber and domains dispersed in the matrix. Each domain contains a cross-linked product of the second rubber and conductive particles. Further, the volume resistivity of each domain is less than the volume resistivity of the matrix.

Further, when a cubic sample having a side of 20.0 μm of the conductive layer is sampled from the outer surface of the conductive layer to a depth of 20.0 μm, 50% by number or more of the entire domains in the cubic sample satisfy the following condition.

< Condition >

Assuming that the domain to be evaluated in the cubic sample is enveloped by an enveloping cuboid having two surfaces each perpendicular to a line segment L passing through at least one arbitrary point in the domain to be evaluated and perpendicular to the surface of the mandrel, "X" is longer than "Y" and "Z", where "X" is the length of the enveloping cuboid in the X-axis direction, "Y" is its length in the Y-axis direction and "Z" is its length in the Z-axis direction, and a line segment S perpendicular to the line segment L and parallel to the X-axis can be drawn.

A charging member according to an aspect of the present disclosure is described below with reference to the drawings.

Fig. 1 is a perspective view of a charging roller 100 according to an aspect of the present disclosure. The charging roller 100 includes a core shaft 101 having a conductive outer surface and a conductive layer 103 covering the outer circumferential surface of the core shaft 101. Fig. 2A and 2B are explanatory views of the configuration of the conductive layer 103 of the charging roller 100, and fig. 2A is a schematic view of a cross section of the conductive layer 103 in a direction perpendicular to the circumferential direction of the charging roller 100 (hereinafter also referred to as "longitudinal direction"). The conductive layer 103 includes a matrix 201 containing a first rubber and domains 203 dispersed in the matrix. Fig. 2B is a schematic diagram for explaining a state of the domain 203 existing in a surface region from the outer surface of the conductive layer to a depth of 20 μm. In fig. 2B, a cross section of the conductive layer 103 in the circumferential direction of the charging roller is denoted by reference numeral 205A, and a cross section of the conductive layer 103 in the longitudinal direction is denoted by reference numeral 205B. In addition, an outer surface of the conductive layer is denoted by reference numeral 207, and the outer surface 207 of the conductive layer is an outer surface of the charging roller, that is, a surface serving as a surface facing the electrophotographic photosensitive member. In addition, each domain 203 contains conductive particles, such as carbon black (not shown).

Next, the domain 203 satisfying the above condition is described with reference to fig. 3. In fig. 3, the dimensions of the mandrel 101 and the domain 203 are not coordinated with each other. A cuboid (hereinafter also referred to as "enveloping cuboid") 301 of the enveloping domain 203 is scaled. The enveloping cuboid 301 is defined as a cuboid whose all six surfaces are in contact with the domain 203. In addition, when a line segment L passing through one arbitrary point in the domain 203 and perpendicular to the surface of the mandrel 101 is drawn, two surfaces of the six surfaces for forming the enveloping rectangular solid 301 are perpendicular to the line segment L. In addition, when the length of the enveloping rectangular solid 301 in the X-axis direction is denoted by "X", the length thereof in the Y-axis direction is denoted by "Y", and the length thereof in the Z-axis direction is denoted by "Z", X "is longer than" Y "and" Z ". In other words, the longest side of the enveloping cuboid 301 is set as the X-axis. At this time, in the field 203 according to the present disclosure, a line segment S parallel to the X axis and perpendicular to the line segment L may be drawn. That is, it can be said that the domain 203 satisfying the condition exists in the conductive layer in a state of specifically extending, for example, in a non-depth direction of the conductive layer, for example, a length direction.

In addition, the volume resistivity of each domain 203 is less than the volume resistivity of the matrix 201. Thus, the domains 203 containing conductive particles are primarily responsible for charge transfer in the conductive layer. Therefore, in the conductive layer including a certain amount of domains each satisfying the above-described conditions, the volume resistivity of each domain 203 is smaller than that of the substrate 201, and therefore even when a triboelectric charge is generated on the surface of the nip portion of the charging roller, the charge can be diffused in the direction in which the domain 203 extends through the domain 203. That is, the transfer direction of the triboelectric charges in the conductive layer can be controlled.

Meanwhile, fig. 4 is an illustration of one example of a domain that does not satisfy a condition. When the longest side 405 of the enveloping cuboid 403 of the domain 401 is arranged as the X-axis in fig. 4, the X-axis is perpendicular to the surface of the mandrel 101. Therefore, when drawing a line segment L that passes through an arbitrary point in the field 401 and is perpendicular to the surface of the mandrel 101, a line segment S that is perpendicular to the line segment L and parallel to the X axis cannot be drawn. Such domains 401 extend from the outer surface of the conductive layer towards the mandrel. In this case, the triboelectric charge generated on the surface of the nip portion remains in the region between the surface of the nip portion and the mandrel, and thus may affect the discharge performance of the charging roller.

< inferior angle formed by line segment P and line segment Q >

The enveloping cuboid comprises a first YZ surface and a second YZ surface facing each other, each surface comprising a Y-axis and a Z-axis. A line segment P is defined as the longest line segment among line segments each connecting a portion of the first YZ plane in contact with the domain and a portion of the second YZ plane in contact with the domain. When drawing a line segment Q having the same starting point as the starting point of the line segment P in the first or second YZ surface and perpendicular to the mandrel surface, the inferior angle formed by the line segment P and the line segment Q is defined as the inferior angle θ, and the mode value of the inferior angle θ of each of all the domains in the cubic sample preferably falls within 60 ° or more and 90 ° or less. In order to immediately transfer the electric charge generated by the frictional charging between the electrophotographic photosensitive member and the charging roller from the nip position of the charging roller to the non-nip position thereof, it is important that the direction in which the domains extend is not oriented toward the depth direction of the conductive layer. Therefore, here, the degree to which the direction in which the domain extends is oriented toward the depth direction is specified.

Fig. 5 is an explanatory diagram showing an inferior angle θ of a direction in which the domain 203 extends according to the present disclosure. When the longest side of the enveloping cuboid 301 is defined as the X-axis, the longest line segment 507 among line segments each connecting a contact point with the domain 203 in a first YZ surface 505 in the enveloping cuboid and a contact point with the domain 203 in a second YZ surface in the enveloping cuboid facing the first YZ surface is a line segment representing the maximum length of the domain. Further, when a line segment 501 passing through a contact point of the line segment 507 with the first YZ plane and perpendicular to the stem 101 is drawn, an inferior angle formed by the line segment 507 and the line segment 501 is represented by θ. When the inferior angle θ is 90 °, it can be said that the domain 203 extends in the tangential direction of the outer surface of the conductive layer 103. As the inferior angle θ decreases from 90 °, the domains 203 extend more in the thickness direction of the conductive layer. Therefore, in order to allow frictional charges generated on the surface of the charging roller to escape from the nip portion to suppress the occurrence of discharge unevenness of the charging roller, the inferior angle θ is preferably set to 60 ° or more and 90 ° or less.

< length of enveloping cuboid in X-axis direction "X" >

The arithmetic average of the lengths "x" of the enveloping cuboids of the respective domains whose envelopes satisfy the above conditions preferably falls within a range of 0.5 μm or more and 15.0 μm or less. When the average value of "x" is 0.5 μm or more, the charge is more efficiently transferred toward the extending direction of the domain satisfying the condition.

Further, when the average value of "x" is 15.0 μm or less, the matrix-domain structure in which each domain independently exists can be maintained. The calculation method of "x" is described in example 1.

< conductive mandrel >

A conductive mandrel appropriately selected from among conductive mandrels known in the field of electrophotographic conductive members can be used as the conductive mandrel 101. Examples of the mandrel material are aluminum, stainless steel, synthetic resin having electrical conductivity, or metal or alloy, such as iron or copper alloy. Further, this material may be subjected to oxidation treatment or plating treatment with chromium, nickel, or the like. Although either of electroplating and electroless plating can be used as the plating method, electroless plating is preferred from the viewpoint of dimensional stability. Examples of the kind of electroless plating used herein may include nickel plating, copper plating, gold plating, and plating with other various alloys. The thickness of the plating layer is preferably 0.05 μm or more, and in view of the balance between the work efficiency and the rust inhibitive ability, the thickness of the plating layer is preferably 0.1 μm to 30 μm. Examples of the shape of the conductive mandrel may be a cylindrical shape or a hollow cylindrical shape. Outer diameter of conductive mandrel

Preferably falling in the range of 3mm to 10 mm.

< conductive layer >

< surface resistance >

The electric charge generated by frictional charging between the electrophotographic photosensitive member and the charging roller is an electric charge generated on the surface of the charging roller. Therefore, the surface shape of the conductive layer preferably has low resistance without impairing the function as a charging roller. Specifically, the surface resistance value measured on the outer surface of the charging roller is preferably set at 1.0 × 10^-1Omega is 1.0X 10 or more³The range of Ω or less. Therefore, the electric charges generated on the surface can be transferred more rapidly.

< substrate >

The matrix contains a cross-linked product of the first rubber. The volume resistivity "m" of the matrix is preferably more than 1,000 times as large as the volume resistivity "d" of each domain described later. When the volume resistivity "m" of the matrix is more than 1,000 times as large as the volume resistivity "d" of each domain, electric charges are transferred to the domain, which is a region having a low resistance in the conductive layer, and transferred along a direction in which the domain extends to the domain adjacent thereto. Therefore, the electric charge generated by the frictional electrification between the electrophotographic photosensitive member and the charging roller is immediately transferred from the nip position of the charging roller to the non-nip position thereof. Therefore, in the charging roller, the potential difference between its nip position with the electrophotographic photosensitive member at the start of rotation and its non-nip position is averaged. The measurement method of the volume resistivity of the matrix is described later.

< first rubber >

The blending ratio of the first rubber is largest in the rubber composition for forming the conductive layer. The crosslinked material of the rubber dominates the mechanical strength of the conductive layer, and therefore a rubber that enables the conductive layer to sufficiently exhibit the strength required for the conductive member for electrophotography after crosslinking thereof is preferably used as the first rubber. Examples of the first rubber include Natural Rubber (NR), Isoprene Rubber (IR), Butadiene Rubber (BR), styrene-butadiene rubber (SBR), butyl rubber (IIR), nitrile-butadiene rubber (NBR), ethylene-propylene rubber (EPM), ethylene-propylene-diene terpolymer rubber (EPDM), Chloroprene Rubber (CR), and silicone rubber.

< reinforcing agent >

The reinforcing agent may be incorporated into the matrix to the extent that it does not affect the conductivity of the matrix. An example of a reinforcing agent is a reinforcing carbon black having low conductivity. Specific examples of reinforcing carbon blacks include Fast Extrusion Furnace (FEF) grade blacks, General Purpose Furnace (GPF) grade blacks, semi-reinforcing furnace (SRF) grade blacks, and MT carbons.

Further, fillers, processing aids, vulcanization accelerators, vulcanization accelerator aids, vulcanization retarder aids, age resisters, softeners, dispersants, colorants, and the like, which are generally used as blending agents for rubbers, may be added to the first rubber for forming the matrix as needed.

< ion conductive agent >

In order to adjust the resistance of the elastic layer of the charging roller within a suitable medium resistance interval of the charging roller (e.g., 1.0 × 10)⁵Ω～1.0×10⁸Ω), an ion conductive agent may be blended in the matrix to such an extent that the agent does not bleed out. For example, inorganic ionic substances, cationic surfactants, amphoteric surfactants, quaternary ammonium salts, and organic acid lithium salts described below can be used as the ion conductive agent.

The inorganic ion substance is lithium perchlorate, sodium perchlorate, calcium perchlorate, etc. The cationic surfactant is lauryl trimethyl ammonium chloride, stearyl trimethyl ammonium chloride, octadecyl trimethyl ammonium chloride, etc. In addition, the cationic surfactant is dodecyl trimethyl ammonium chloride, hexadecyl trimethyl ammonium chloride, and the like. Further, the cationic surfactant is trioctylpropylammonium bromide, modified aliphatic dimethylethylammonium ethylsulfate, or the like. The amphoteric surfactant is lauryl betaine, stearyl betaine, dimethyl alkyl lauryl betaine, etc. The quaternary ammonium salt is tetraethylammonium perchlorate, tetrabutylammonium perchlorate, trimethyloctadecyl ammonium perchlorate and the like. The organic acid lithium salt is lithium trifluoromethanesulfonate and the like.

The blending amount of the ionic conductive agent is, for example, 0.5 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the rubber composition.

< roughening particles >

Spherical particles each having a particle diameter in the range of, for example, 1 μm to 90 μm may be added to the rubber composition for forming the matrix. Examples of particles are at least one spherical particle selected from the following:

phenolic resin particles, silicone resin particles, polyacrylonitrile resin particles, polystyrene resin particles, polyurethane resin particles, nylon resin particles, polyethylene resin particles, polypropylene resin particles, acrylic resin particles, silica particles, and alumina particles. When such a rubber composition is used, a convex portion derived from spherical particles can be formed on the outer surface of the elastic layer.

< Domain >

The domain 203 includes a cross-linked product of the second rubber and conductive particles. Here, "conductivity" is defined as having less than 1.0X 10⁸Volume resistivity of Ω · cm.

< second rubber >

Specific examples of the rubber usable as the second rubber include the following rubbers:

NR, IR, BR, SBR, IIR, NBR, EPM, EPDM, CR, silicone rubber, and Urethane Rubber (UR).

< conductive particles >

Examples of the conductive particles include electron conductive agents including: carbon materials such as conductive carbon black and graphite; conductive oxides such as titanium oxide and tin oxide; metals such as Cu and Ag; and particles made conductive by coating their surfaces with a conductive oxide or metal. These conductive particles can be used by blending in an appropriate amount. Among them, conductive carbon black is preferably used as the conductive particles. Specific examples of the conductive carbon black include gas furnace carbon black, oil furnace carbon black, thermal black, lamp black, acetylene black, and ketjen black (ketjen black).

< volume resistivity >

In order to control the flow of charges with the domains containing the conductive particles, the volume resistivity "d" of each domain is preferably as low as 1,000 times or more the volume resistivity "m" of the matrix. Accordingly, electric charges are more easily transferred in each domain than in the matrix, whereby electric charges are transferred along the direction in which each domain extends. A specific measurement method of the volume resistivity of each domain is described in example 1.

The thickness of the conductive layer is not particularly limited, but may be preferably 0.5mm (500 μm) to 5 mm.

< Process Cartridge >

Fig. 8 is a schematic sectional view of a process cartridge for electrophotography including a charging roller according to one embodiment of the present disclosure. The process cartridge 800 shown in fig. 8 is formed by integrating a developing device and a charging device as a main body detachably mountable to an electrophotographic image forming apparatus. The developing device is obtained by integrating at least the developing roller 803, the toner container 806, and the toner 809. The photosensitive drum 801 is an example of an electrophotographic photosensitive member. The charging roller 802 is configured to be able to charge the photosensitive drum 801. The developing device may include a toner supply roller 804, a developing blade 808, and an agitating blade 810 as necessary. The charging device is obtained by integrating at least the photosensitive drum 801 and the charging roller 802. A cleaning blade 805 for removing residual toner on the photosensitive drum 801 is disposed adjacent to the photosensitive drum 801. In addition, the charging device includes a waste toner container 807 for recovering the residual toner that has been removed. A voltage is applied to each of the charging roller 802, the developing roller 803, the toner supply roller 804, and the developing blade 808.

< electrophotographic image forming apparatus >

Fig. 9 is a schematic configuration diagram of an electrophotographic image forming apparatus 900 using a charging roller according to one embodiment of the present disclosure. The electrophotographic image forming apparatus 900 shown in fig. 9 is formed such that 4 process cartridges 800 are assembled to be detachably mounted thereto. Each process cartridge 800 corresponds to each color of Black (BK), magenta (M), yellow (Y), and cyan (C), and toner having the corresponding color is used therein. Each process cartridge 800 has the same configuration except that the colors of the toners used therein are different from each other.

The configuration of each process cartridge 800 is substantially the same as that shown in fig. 8. The process cartridges 800 each include a photosensitive drum 801, a charging roller 802, a developing roller 803, a toner supply roller 804, a cleaning blade 805, a toner container 806, a waste toner container 807, a developing blade 808, toner 809, and an agitating blade 810.

The photosensitive drum 801 rotates in a direction indicated by an arrow, and is uniformly charged by a charging roller 802 to which a voltage is applied from a charging bias power supply (not shown). Irradiating the surface of the photosensitive drum 801 with the exposure light 911 results in forming an electrostatic latent image on the surface. Meanwhile, the toner 809 stored in the toner container 806 is supplied to the toner supply roller 804 by the stirring blade 810. The toner supply roller 804 supplies toner 809 to the developing roller 803. The top of the surface of the developing roller 803 is uniformly coated with toner 809 by a developing blade 808 arranged in contact with the developing roller 803, and an electric charge is imparted to the toner 809 by triboelectric charging. The electrostatic latent image is developed by application of toner 809 conveyed by a developing roller 803 arranged in contact with the photosensitive drum 801, and visualized as a toner image.

The visualized toner image on the photosensitive drum is transferred onto the intermediate transfer belt 915 by the primary transfer roller 912, and a voltage is applied to the intermediate transfer belt 915 by a primary transfer bias power source. The intermediate transfer belt 915 is driven while being supported by the tension roller 913 and the intermediate transfer belt driving roller 914. The toner images of the respective colors are sequentially superposed to form a color image on the intermediate transfer belt 915.

The transfer material 919 is fed into the apparatus by a sheet feeding roller. The transfer material 919 is conveyed into a space between the intermediate transfer belt 915 and the secondary transfer roller 916. A voltage is applied from the secondary transfer bias power source to the secondary transfer roller 916, thereby transferring the color image on the intermediate transfer belt 915 onto the transfer material 919. The transfer material 919 to which the color image has been transferred is subjected to a fixing process by a fixing unit 918. The transfer material 919 subjected to the fixing process is discharged to the outside of the apparatus.

Meanwhile, the toner remaining on the photosensitive drum 801 without being transferred is scraped off by the cleaning blade 805 to be stored in the waste toner storage container 807. Further, the toner remaining on the intermediate transfer belt 915 without being transferred is scraped off by a cleaning device 917 for the intermediate transfer belt.

< method for producing charging roller >

A method including the following steps (a) to (D) is described as a non-limiting example of a production method of a charging roller according to an aspect of the present disclosure:

step (A): a step of preparing a carbon master batch for domain formation (hereinafter also referred to as "CMB") containing carbon black and rubber;

step (B): a step of preparing a rubber composition (hereinafter also referred to as "MRC") used as a matrix;

step (C): a step of mixing the carbon master batch and the rubber composition to prepare a rubber composition having a matrix-domain structure; and

step (D): a step of coating the outer periphery (surface) of the mandrel with a rubber composition having a matrix-domain structure.

Regarding factors for determining the domain diameter D in a matrix-domain Structure in which two incompatible polymers are melted and kneaded, Taylor's equation, Wu's empirical equation, and Timentian's equation (see Sumitomo Chemical's R & DREPorts,2003-II, pages 44-45, "Structure Control by Kneading") described below are known.

Taylor equation

D＝[C·σ/ηm·γ]·f(ηm/ηd) (1)

Wu's empirical equation

γ·D·ηm/σ＝4(ηd/ηm)0.84·ηd/ηm>1 (2)

γ·D·ηm/σ＝4(ηd/ηm)-0.84·ηd/ηm<1 (3)

Equation of time field

In equations (1) to (4), D represents the domain diameter (maximum feret diameter Df) of CMB, C represents a constant, σ represents surface tension, η m represents the viscosity of the matrix, and η D represents the viscosity of each domain. In addition, γ represents the shear rate, η represents the viscosity of the mixed system, P represents the probability of collisional coalescence,

the EDK represents the phase volume of the domain and the phase cleavage energy of the domain.

As can be seen from equations (1) to (4), it is effective to control the physical properties of, for example, CMB and MRC and the kneading conditions in step (B) for controlling the domain diameter D of CMB. Specifically, the control of the following four items (a) to (d) is effective:

(a) the difference between the surface tensions σ of CMB and MRC;

(b) the ratio (η m/η d) between the viscosity (η d) of the CMB and the viscosity (η m) of the MRC;

(c) shear rate (γ) and energy value (EDK) at shear in mixing CMB and MRC in step (B); and

(d) volume fraction of CMB to MRC in step (B).

Now, items (a) to (d) are described in detail.

(a) The difference in interfacial tension between the CMB and the MRC;

generally, phase separation occurs when two immiscible rubbers are mixed with each other. The reason for this is as follows. The interaction between similar polymers is stronger than that between different polymers, and thus the similar polymers aggregate with each other to lower the free energy, thereby being stabilized. The interface of the phase separation structure is in contact with a different polymer, and thus its free energy becomes higher than that of the inside stabilized due to the interaction between similar polymers. As a result, interfacial tension for reducing an area in contact with different polymers is generated so as to lower the free energy of the interface. When the interfacial tension is small, even different polymers attempt to be uniformly mixed with each other to increase entropy. The homogeneously mixed state means dissolution, and a Solubility Parameter (SP) value and an interfacial tension serving as a solubility guide tend to be correlated with each other. Specifically, it is considered that the difference in interfacial tension between the CMB and the MRC is correlated with the difference in SP value between the CMB and the MRC. Therefore, the above difference can be controlled by changing the combination of MRC and CMB.

The difference between the absolute values of the solubility parameters was 0.4 (J/cm)³)^0.5Above and 4.0 (J/cm)³)^0.5Such rubbers below are preferably selected as the first rubber in the MRC and the second rubber in the CMB. The difference in absolute value of the solubility parameter is more preferably 0.4 (J/cm)³)^0.5Above and 2.2 (J/cm)³)^0.5The following. When the above difference falls within such a range, a stable phase separation structure can be formed.

< method for measuring SP value >

By making a calibration curve using a material of which the SP value is known, the SP values of MRC and CMB can be calculated with satisfactory accuracy. The catalog value of the material manufacturer may also be used as the known SP value. For example, the SP value of each of NBR and SBR is determined substantially by the content ratio of acrylonitrile and styrene, regardless of the molecular weight thereof.

Therefore, the SP value of each rubber used to form the matrix and the domain can be calculated from a calibration curve obtained from a material of which the SP value is known by analyzing the content ratio of acrylonitrile or styrene of the rubber.

Here, analytical methods such as pyrolysis gas chromatography (Py-GC) and solid-state NMR can be used for the analysis of the content ratio of acrylonitrile or styrene, respectively. In addition, the SP value of the isoprene rubber is determined depending on the structure of isomers, such as 1, 2-polyisoprene, 1, 3-polyisoprene, 3, 4-polyisoprene, cis-1, 4-polyisoprene, trans-1, 4-polyisoprene, etc. Therefore, as in SBR and NBR, the SP value of isoprene rubber can be calculated from a material of which the SP value is known by analyzing its isomer content ratio by Py-GC and solid-state NMR, for example.

(b) Viscosity ratio between CMB and MRC;

as the viscosity ratio (η d/η m) between CMB and MRC approaches 1, the maximum Ferrett diameter of each domain decreases. The viscosity ratio between the CMB and the MRC can be adjusted by selecting the respective Mooney viscosities of the CMB and the MRC or selecting the kind and blending amount of the filler. The viscosity ratio may be adjusted to such an extent that the formation of a phase separation structure is not inhibited by adding a plasticizer such as paraffin oil. The viscosity ratio can also be adjusted by adjusting the temperature during kneading. The viscosity of each of the rubber mixture for forming the domains and the rubber mixture for forming the matrix was obtained by measuring the mooney viscosity ML (1+4) at the rubber temperature at the time of kneading in accordance with JIS K6300-1: 2013.

(c) Shear rate when mixing MRC and CMB and energy value when shearing;

when the shear rate at the time of kneading MRC and CMB is high, and when the energy value at the time of shearing is large, the maximum feret diameter Df of each domain is reduced.

The shear rate can be increased by increasing the inner diameter of the stirring member of the mixer, such as a blade or a screw, to reduce the clearance from the end face of the stirring member to the inner wall of the mixer, or by increasing the number of rotations of the stirring member. Further, the energy value at the time of shearing can be increased by increasing the number of rotations of the stirring member, or by increasing the viscosity of each of the first rubber in CMB and the second rubber in MRC.

(d) Volume fraction of CMB to MRC;

the volume fraction of CMB to MRC is related to the probability of collision and coalescence of the rubber mixture used to form the domains and the rubber mixture used to form the matrix. Specifically, the reduction in the volume fraction of the rubber mixture for forming the domains to the rubber mixture for forming the matrix reduces the probability that the rubber mixture for forming the domains and the rubber mixture for forming the matrix collide with each other and coalesce. In other words, the size of the domains decreases as the volume fraction of the domains in the matrix decreases to the extent that the desired conductivity is obtained.

In the above step (C), CMB serving as a domain and MRC serving as a matrix are kneaded to produce an unvulcanized rubber composition having a matrix-domain structure. Examples of the production method of the composition may include the methods described in the following (C1) and (C2).

(C1) The raw materials of each of the CMB used as the domain and the unvulcanized rubber composition used as the matrix are mixed with an internal mixer such as a Banbury mixer or a pressure mixer. Thereafter, the CMB used as the domain, the unvulcanized rubber composition used as the matrix, and the raw materials such as the vulcanizing agent or the vulcanization accelerator are kneaded with an open mixer such as an open roll to be integrated.

(C2) The raw materials of the CMB used as the domain are mixed by an internal mixer such as a banbury mixer or a pressure mixer. Thereafter, CMB used as the domain and raw materials of the unvulcanized rubber composition used as the matrix were mixed by an internal mixer. Finally, the mixture and the raw materials such as a vulcanizing agent or a vulcanization accelerator are kneaded with an open mixer such as an open roll to be integrated.

Examples of the method of coating the outer circumference of the mandrel with the rubber composition having a matrix-domain structure in the above-mentioned step (D) may include the methods described in the following (D1) and (D2):

(D1) extrusion molding, which includes extruding a rubber composition having a matrix-domain structure from a crosshead together with a mandrel to coat the outer periphery of the mandrel with the rubber composition having a matrix-domain structure; and

(D2) mold forming, which includes coating an outer periphery of a mandrel disposed in a forming mold with a rubber composition having a matrix-domain structure by using the forming mold.

Fig. 6 is a schematic configuration diagram of an extrusion molding machine 600 including a crosshead used in the extrusion molding according to (D1). The extruder 600 coats the entire periphery of the mandrel 601 with an unvulcanized rubber composition 602 so that the composition has a uniform thickness, thereby producing an unvulcanized rubber roller 603.

The extrusion molding machine 600 is provided therein with a crosshead 604 into which the mandrel 601 and the unvulcanized rubber composition 602 are fed, a conveying roller 605 for feeding the mandrel 601 into the crosshead 604, and a cylinder 606 for feeding the unvulcanized rubber composition 602 to the crosshead 604.

The mandrel 601 is continuously introduced into a crosshead 604 by a feed roller 605. The barrel 606 itself includes a screw 607, and the screw 607 is rotated to introduce the unvulcanized rubber composition 602 into the crosshead 604.

For each mandrel 601 introduced into the crosshead 604, the outer circumferential surface of the mandrel 601 is coated with an unvulcanized rubber composition 602 introduced into the crosshead 604 from a cylinder 606. Then, an unvulcanized rubber roller 603 obtained by coating the outer peripheral surface of the mandrel 601 with an unvulcanized rubber composition 602 is fed from a die 608 serving as an outlet of the cross head 604.

When the charging roller according to the present disclosure is produced by the method according to (D1), the extension state of the domains can be controlled by, for example, the material, the kneading conditions, and the extrusion conditions.

First, as described above, the maximum Ferrett diameter Df of each domain in the matrix-domain structure can be controlled by the materials used for MRC and CMB and their mixing conditions. As the maximum feret diameter Df of each domain becomes larger, the length "X" in the X-axis direction of the enveloping rectangular parallelepiped of the extended domain formed by the step of extruding the rubber composition having the matrix-domain structure becomes longer. Therefore, in order to set the length "X" of the enveloping rectangular solid of the extended domain in the X-axis direction as a target value, the viscosity ratio between CMB and MRC and the shear rate at the time of kneading need only be appropriately adjusted depending on the polymer used.

Next, the extrusion conditions are described. The inferior angle θ formed by the line segment P and the line segment Q shown in fig. 5 can be adjusted by adjusting the flow rate of the rubber composition, the inner diameter of the extruder die, and the thickness of the rubber composition layer in the extrusion step in which the rubber composition having the matrix-domain structure is co-extruded with the mandrel from the cross-head to form the rubber composition layer on the outer circumferential surface of the mandrel. The inferior angle θ can be made close to 90 ° by applying a larger shear stress (shear) to the rubber composition, for example, in the process of forming the rubber composition layer on the outer peripheral surface of the mandrel. Examples of the method of increasing the shear stress to be applied to the rubber composition in the extrusion step using the crosshead include decreasing the inner diameter of the die and increasing the flow rate of the rubber composition. When the inner diameter of the die is decreased, the rubber composition to be extruded onto the outer peripheral surface of the mandrel is extended with a greater force. At this time, a larger shearing force may be applied to the thickness region to a depth of 20.0 μm from the surface opposite to the side of the rubber composition layer contacting the outer circumferential surface of the mandrel. Therefore, the plurality of domains existing in the region may extend in the direction along the moving direction of the mandrel, and as a result, 50% by number or more of all the domains in the 20.0 μm cubic sample on the side from which the region is sampled may each satisfy the condition.

Next, the layer of the unvulcanized rubber composition obtained by the above step (D), which contains the domains extending in the direction along the moving direction of the mandrel, is then converted into the conductive layer by the vulcanization step as the step (E). Therefore, the charging roller according to the aspect can be obtained. Specific examples of the method of heating the rubber composition layer may include heating with a hot air furnace heated by a kirk oven (gear oven), heating and vulcanizing with far infrared rays, and heating with vulcanizer steam. Among them, hot-air furnace heating or far-infrared heating is preferable because they are suitable for continuous production.

The outer surface of the conductive layer according to the present disclosure formed by the above method is preferably not ground, and the layer contains domains each extending in a predetermined direction such that domains existing in a larger amount on a side close to the outer surface of the conductive layer do not disappear, the domains each extending such that the inferior angle θ is 90 ° or less. Alternatively, even when polishing is performed, it is preferable to perform polishing in such a manner that loss of domains existing in a larger amount, each extending so that the inferior angle θ is 90 ° or less, is suppressed as much as possible on the side close to the outer surface of the conductive layer. Therefore, when the outer shape of the elastic layer of the charging roller according to this aspect is shaped into a crown shape, extrusion molding is performed in consideration of such grinding. The outer shape of the unvulcanized rubber layer is preferably molded into a crown shape by controlling, for example, the speed at which the core shaft is extruded from the crosshead and the speed at which the unvulcanized rubber composition is extruded therefrom in extrusion molding. Specifically, it is preferable to change the relative ratio between the speed at which the mandrel 601 is fed by the conveying roller 605 and the speed at which the unvulcanized rubber composition is fed from the cylinder 606. At this time, the speed at which the unvulcanized rubber composition 602 is fed from the cylinder 606 to the crosshead 604 is made constant. The thickness of the layer of unvulcanized rubber composition 602 formed on the outer peripheral surface of the mandrel 601 is determined by the ratio between the feeding speed of the mandrel 601 and the feeding speed of the unvulcanized rubber composition 602. Thus, the elastic layer can be formed into a crown shape without any grinding. In the mold forming, it is preferable to perform slight grinding with a crown-shaped mold to form the outer shape of the unvulcanized rubber layer into a crown shape. The crown shape is a shape in which the outer diameter of the elastic layer is larger at the center portion than at the end portions in the longitudinal direction of the mandrel.

The vulcanized rubber composition in both end portions of the vulcanized rubber roller is removed in a subsequent different step. Thus, the vulcanized rubber roller is completed. Thus, in the completed vulcanized rubber roller, both end portions of the mandrel are exposed.

The surface layer of the vulcanized rubber roller may be surface-treated based on irradiation with UV light or electron beam to the extent that the matrix-domain structure and the shape of the domains are not affected.

According to an aspect of the present disclosure, a charging roller useful for stably forming high-quality electrophotographic images under various environments can be obtained. Further, according to another aspect of the present disclosure, a process cartridge useful for stably providing an electrophotographic image of high quality can be obtained. Further, according to another aspect of the present disclosure, an electrophotographic image forming apparatus capable of stably forming an electrophotographic image of high quality can be obtained.

[ examples ]

The following materials were prepared as materials used in producing the charging rollers according to examples and comparative examples.

<NBR>

N230SV (trade name: JSR NBR N230SV, manufactured by JSR Corporation)

DN401LL (trade name: Nipol DN401LL, manufactured by ZEON Corporation)

<SBR>

T2003 (trade name: Tufdene 2003, manufactured by Asahi Kasei Corporation)

A303 (trade name: Asaprene 303, manufactured by Asahi Kasei Corporation)

< Chloroprene Rubber (CR) >

B31 (trade name: SKYPRENE B31, manufactured by Tosoh Corporation)

<EPDM>

E505A (trade name: Esprene 505A, manufactured by Sumitomo Chemical Co., Ltd.)

< Butadiene Rubber (BR) >

BR150B (trade name: UBEPOL BR150B, manufactured by Ube Industries, Ltd.)

< Isoprene Rubber (IR) >

IR2200L (trade name: Nipol IR2200L, manufactured by ZEON Corporation)

< conductive particles >

#7270 (trade name: TOKABLACK #7270SB, manufactured by Tokai Carbon Co., Ltd.)

#44 (trade name: #44, manufactured by Mitsubishi Chemical Corporation)

#7360 (trade name: TOKABLACK #7360SB, manufactured by Tokai Carbon Co., Ltd.)

#5500 (trade name: TOKABLACK #5500SB, manufactured by Tokai Carbon Co., Ltd.)

< vulcanizing agent >

Sulfur (trade name: SULFAX PMC, manufactured by Tsuummi Chemical Industry Co., Ltd.)

< vulcanization accelerators >

TBzTD (trade name: Sanceler TBZTD, manufactured by Sanshin Chemical Industry Co., Ltd.)

TBSI (trade name: SANTOCURE-TBSI, manufactured by FlexSys Inc.)

TS (trade name: Sanceler TS, manufactured by Sanshin Chemical Industry Co., Ltd.)

CZ (trade name: Nocceler CZ-G, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

TOT (trade name: Nocceler TOT-N, manufactured by Ouchi Shinko Chemical Industrial Co., Ltd.)

< vulcanization accelerator Assistant >

ZnO (trade name: Zinc Oxide Type 2, manufactured by Sakai Chemical Industry Co., Ltd.)

< roughening particles >

PMMA particles (trade name: SE-010T, manufactured by Negami Chemical Industrial Co., Ltd., average particle diameter: 10 μm)

Polyethylene particles (trade name: Mipelon XM-221U, manufactured by Mitsui Chemicals, Inc., average particle diameter: 25 μm)

Polyurethane particles (trade name: GRANDPEARL GU-2000P, manufactured by Aica Kogyo Company, Limited, average particle diameter: 20 μm)

< reinforcing Material >

MT carbon (trade name: Thermax Floform N990, manufactured by CanCarb Limited)

[ example 1]

< preparation of Carbon Masterbatch (CMB)1 >

The formulation of the Carbon Masterbatch (CMB) feedstock is shown in table 1. The blending amounts shown in table 1 respectively represent the blending amounts when the amount of SBR used is set to 100 parts by mass. The Carbon Master Batch (CMB) raw materials shown in table 1 were mixed in the blending amounts shown in table 1 to prepare CMB 1. A6-liter pressure mixer (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used as the mixer. Mixing was carried out at a fill rate of 70 vol%, a blade rotation number of 30rpm and 16 minutes.

TABLE 1

< preparation of unvulcanized rubber composition 1 >

The formulation of MRC raw materials used in the preparation of the rubber composition for a kneading is shown in table 2. The blending amounts shown in table 2 respectively represent blending amounts when the usage amount of NBR is set to 100 parts by mass. The raw Materials (MRC) shown in table 2 were added to CMB 1, and the mixture was kneaded to provide a kneaded rubber composition. At this time, the mixing ratio between CMB 1 and MRC is as follows: the amount of SBR used for CMB 1 was set to 25 parts by mass relative to 75 parts by mass of NBR used in MRC. A6-liter pressure mixer (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) was used as the mixer. Mixing was carried out at a fill rate of 70 vol%, a blade rotation number of 30rpm and 16 minutes.

TABLE 2

The raw material formulation for preparing the B-compounded rubber composition is shown in table 3. The raw materials shown in table 3 were added to 100 parts by mass of the a-kneaded rubber composition obtained in the foregoing, and the mixture was further kneaded to provide an unvulcanized rubber composition 1 serving as a B-kneaded rubber composition. Open rolls each having a roll diameter of 12 inches (0.30m) were used as the mixer. The mixing was carried out under the following conditions: the mixture was cut bidirectionally 20 times with a front roll revolution of 10rpm, a rear roll revolution of 8rpm and a roll gap of 2mm, and then subjected to thin passing (light milling)10 times with a roll gap of 0.5 mm.

TABLE 3

< formation of vulcanized rubber layer >

First, a mandrel having an adhesive layer to which a vulcanized rubber layer is adhered is obtained. Specifically, a cylindrical conductive mandrel having a diameter of 6mm and a length of 252mm was used. The mandrel is made of steel and the surface of the mandrel is plated with nickel.

An electrically conductive vulcanized adhesive (trade name: METALOC U-20; manufactured by Toyokagaku Kenkyusho co., ltd.) was applied to the central portion of the mandrel in the axial direction thereof, and dried at 80 ℃ for 30 minutes. The portion of the central portion to which the curing adhesive was applied had a width of 222 mm.

The unvulcanized rubber composition 1 prepared above was co-extruded with a mandrel having an adhesive layer with an extrusion molding machine having a crosshead attached at its tip end to form a layer of the unvulcanized rubber composition 1 on the outer peripheral surface of the mandrel. Thus, a crown-shaped unvulcanized rubber roller was obtained. The molding temperature, the inner diameter of the cylinder 606 of the machine and the number of rotations of the extrusion screw were set to 100 ℃, 70mm and 20rpm, respectively, and the flow rate of the rubber composition 1 to be introduced into the crosshead from the cylinder was set to 53m/sec (the flow rate was calculated from the weight of the rubber portion of the molded unvulcanized rubber roll). Further, the inner diameter of the die of the crosshead was 8.0 mm. In addition, in order to control the outer diameter of the center of the unvulcanized rubber roller in the direction along the axis thereof and the outer diameters of the ends in that direction while changing the feed speed of the mandrel, the unvulcanized rubber roller is shaped so that the outer diameter of the unvulcanized rubber roller becomes thicker than the inner diameter of the die. Specifically, the outer diameter of the center of the unvulcanized rubber roller in the direction along the axis thereof was set to 8.6mm, and the outer diameters of the ends in this direction were set to 8.5mm, respectively. Thereafter, heating was performed in a hot air oven at a temperature of 190 ℃ for 60 minutes to vulcanize the layer of the unvulcanized rubber composition 1. Thus, a vulcanized rubber layer was obtained. Both end portions of the vulcanized rubber layer were cut so that the length thereof in the axial direction became 232 mm. Thus, a vulcanized rubber roller was obtained.

< vulcanized rubber layer after extrusion by UV light irradiation >

Surface of vulcanized rubber roller obtained by UV light irradiationAnd (5) kneading. Thus, the charging roller 1 having the UV-treated region on the surface of the elastic layer (surface layer) thereof was obtained. A low-pressure mercury lamp (trade name: GLQ500US/11, manufactured by Toshiba Lighting) was used in the UV irradiation&Technology Corporation), and the vulcanized rubber roller is uniformly irradiated with UV light while rotating. When the measurement was performed using the sensitivity of the sensor corresponding to the 254nm wavelength, the amount of UV light was set to 9,000mJ/cm²。

< measurement of surface resistance value of charging roller >

The produced charging roller was left to stand for 24 hours in an environment at a temperature of 23 ℃ and a relative humidity of 50%. Thereafter, under the same environment, a direct voltage of 100V was applied to the roller with the following meter and probe while the pressure of each of the probes against the roller was set to 10 μ N, and then a current was measured for 1 second after applying a voltage for 2 seconds at a sampling period of 100 Hz. Measurements were made at three points: the conductive layer of the roller has a center position in a length direction thereof and positions +90mm and-90 mm from the center position in the length direction. Further, measurement of each point was performed every 90 ° in the circumferential direction of the roll. The arithmetic average of the measurement values obtained at 12 points was defined as the surface resistance value of the charging roller.

High resistance meter (trade name: Model 6517B Electrometer, Keithley Instruments)

Probe (200 μm pitch, two probes)

The surface resistance values obtained by the above measurements are shown in table 5 (table 5 is shown in the last part of the following description).

< identification of the Presence of Domain and measurement of Domain shape >

The three-dimensional reconstruction of the rubber sheet cut from the charging roller was performed by using FIB-SEM with a low temperature system. Helios G4 UC (manufactured by Thermo Fisher Scientific) and Cryo Transfer System PP3010T (manufactured by Quorum Technologies) can be used as FIB-SEM with cryogenic System. The resulting three-dimensional reconstruction data was analyzed using image analysis software (AVIZO, manufactured by Thermo Fisher Scientific), and then the presence or absence of the domain presence and the measurement of the domain shape were identified. The specific treatment is as follows.

The length direction of the charging roller is denoted by "a-axis", and the tangential direction of the circular arc drawn by the surface of the roller in a roller section perpendicular to the length direction of the "a-axis" is denoted by "b-axis". The razor blade was brought into perpendicular contact with the roller surface to cut the surface, so that a quadrangle having a width of 5mm in the "b-axis" direction and a length of 5mm in the "a-axis" direction centered on the contact point between the circular arc and the tangent line could be formed. Finally, the portion of the roller in contact with the mandrel was cut in a shape along the mandrel, thereby producing a rubber sheet measuring 5mm in the "a-axis" direction × 5mm in the "b-axis" direction and having a thickness corresponding to that of the vulcanized rubber layer.

The rubber sheet was cut out from 12 points (including every 90 ° in the circumferential direction of the charging roller, and the center position in the length direction of the charging roller and the positions +90mm and-90 mm from the center position). Thus, a total of 12 rubber sheets were prepared.

Each rubber sheet was adhered with silver paste to a cylindrical stub of copper of 10mm diameter so that part of it already being the roller surface faced upwards. The resultant was dried at room temperature (25 ℃) for 1 hour to provide an observation sample.

Three-dimensional reconstruction of the sample was observed by using FIB-SEM (apparatus name: Helios G4 UC, manufactured by Thermo Fisher Scientific, and Cryo Transfer System PP3010T, manufactured by Quorum Technologies) with a cryogenic System.

That is, the observation sample was cooled to-170 ℃ by using a cryogenic system. Then, the frozen observation sample was processed by a Focused Ion Beam (FIB) so that a square section of 20.0 μm from the surface of the observation sample (corresponding to the outer surface of the charging roller) to the side of the depth direction (hereinafter referred to as "c direction") and 20.0 μm from the side of the b-axis direction was obtained. The square cross-section may be referred to as the "first b-c surface". At this time, FIB processing was performed under conditions of an acceleration voltage of 30kV and a current of 1.6 nA. Next, SEM images of the first b-c surface were obtained. Here, the surface directly below the protective film in the "b" direction is defined as an observation surface C. The observation surface C was observed by SEM. Observation was performed under the conditions of an acceleration voltage of 350V and a current of 13pA by using a secondary electron image. The first b-c surface was then cut 100nm along the a-axis direction to expose a second b-c surface. Then, SEM images of the second b-c surface were obtained. The cutting of the observed b-c surface was repeated, and SEM images of the newly exposed b-c surface were obtained such that the cutting amount in the a-axis direction reached 20.0 μm, and 200 SEM images of the b-c surface were obtained. By using these SEM images, three-dimensional reconstruction was performed using image analysis software (AVIZO, manufactured by Thermo Fisher Scientific) so that a cubic sample of the conductive layer having a side length of 20.0 μm was reconstructed from a region of the outer surface of the conductive layer to a depth of 20.0 μm.

All the fields observed in the 12 reconstructed three-dimensional images are enveloped by imaginary enveloping cuboids each having two surfaces, each surface being perpendicular to a line segment L passing through at least one arbitrary point in the respective field and perpendicular to the surface of the mandrel. Among three tree axes (tree axes) constituting each enveloping rectangular solid, an axis to which the longest side belongs is defined as an X axis, and the other two axes to which the other two sides belong are defined as a Y axis and a Z axis. Further, the domain enveloped by the enveloping cuboid is a domain completely contained in the three-dimensional image. That is, only a part of the domain contained in the three-dimensional image does not fit the envelope of the enveloping cuboid. By using an enveloping cuboid, the following three terms are calculated.

The number of domains extended%

A plurality of enveloping cuboids satisfying the condition (i.e., capable of drawing a line segment S perpendicular to the line segment L and parallel to the X axis) are counted in all the enveloping cuboids in the 12 three-dimensional images. Then, the counted number is divided by the total number of enveloping cuboids, and the number% of extended domains is obtained.

Inferior angle θ formed by line segment P and line segment Q

For the entire enveloping cuboid, a segment longest in a segment connecting a portion of the first YZ surface in contact with the enveloping domain and a portion of the second YZ surface in contact with the enveloping domain is defined as a segment P, and a segment Q having the same origin as the segment P and perpendicular to the mandrel surface in the first or second YZ surface is drawn. Then, the inferior angle θ, which is defined as the inferior angle formed by the line segment P and the line segment Q, is measured. After that, a histogram showing the relationship between the inferior angle θ ranging from 0 ° to 90 ° in the interval of 10 ° and the number of enveloping cuboids belonging to each category was created (fig. 7). In the histogram, the mode of the inferior angle is defined as the inferior angle θ of the charging roller evaluated.

Average of the length "X" of the enveloping cuboid in the X-axis direction

For an enveloping rectangular solid on which the line segment S can be drawn, the length "X" on the X axis thereof is measured, and the arithmetic average thereof is calculated. This value is a parameter showing the degree of extension of the field of the charging roller extending in the longitudinal direction evaluated.

These results are shown in table 5.

< measurement of volume resistivity ratio m/d between matrix and domain >

The following measurements were made to evaluate the volume resistivity of the matrix in the conductive layer. A Scanning Probe Microscope (SPM) (trade name: Q-Scope 250, manufactured by Quantum Instrument Corporation) was operated in a contact mode.

First, an extremely thin cut piece having a thickness of 1 μm was cut out from the conductive layer of the conductive member A1 at a cutting temperature of-100 ℃ with a microtome (trade name: Leica EM FCS, manufactured by Leica Microsystems). When cutting an extremely thin cut piece, the cut is made in a cross-sectional direction perpendicular to the longitudinal direction of the conductive member in consideration of the direction in which electric charges are transported for discharge. Next, the extremely thin cut sheet was placed on a metal plate in an environment at a temperature of 23 ℃ and a relative humidity of 50%. Then, a portion directly contacting the metal plate is selected, and the cantilever of the SPM is brought into contact with a portion corresponding to the substrate. In this state, a voltage of 50V was applied to the cantilever for 5 seconds, a current value was measured, and then an arithmetic average of the values measured during 5 seconds was calculated.

The surface shape of the measurement slice is observed with SPM and the thickness of the measurement site is calculated from the resulting height profile. Further, the area of the substrate was calculated from the observation result of the surface shape. The volume resistivity is calculated from the thickness and area of the matrix and is defined as the volume resistivity "m" of the matrix.

The conductive layer of the conductive member a1 (length in the longitudinal direction: 232mm) was divided into five equal parts in the longitudinal direction, and further divided into four equal parts in the circumferential direction thereof. Slices were made from any one point in each of the obtained regions, i.e., from a total of 20 points, and then measurements were made. The average of the measured values is defined as the volume resistivity "m" of the matrix.

In order to evaluate the volume resistivity "d" of each domain in the conductive layer, the volume resistivity "d" of each domain was measured by the same method except that in the measurement of the volume resistivity "m" of the matrix described above, the measurement was performed at a site corresponding to an extremely thin slice of the domain, and the voltage at the time of measurement was set to 1V.

The volume resistivity ratio m/d between the matrix and the domains calculated from the volume resistivity "m" of the matrix thus obtained and the volume resistivity "d" of each domain is shown in table 5.

< evaluation of horizontal stripe image >

An electrophotographic image forming apparatus (trade name: LaserJet M608dn, manufactured by Hewlett-Packard Company) was prepared. For evaluation in high-speed processing, the electrophotographic image forming apparatus was modified so that the number of sheets to be output per unit time became 80 sheets of a 4-sized paper per minute, which was larger than the number of original sheets to be output.

First, in order to adapt the roller, the apparatus, and the cartridge to the measurement environment, the charging roller, the electrophotographic image forming apparatus, and the process cartridge were left in an environment at a temperature of 15 ℃ and a relative humidity of 10% for 48 hours.

Next, a charging roller is incorporated as the charging roller of the process cartridge.

The halftone image is output with the apparatus and cartridge, and the output image is evaluated. At the time when the electrophotographic photosensitive member of the cartridge starts to rotate, electric charge is generated at the nip position between the electrophotographic photosensitive member and the charging roller by frictional charging between the electrophotographic photosensitive member and the charging roller. The charge is transferred from the surface of the charging roller to a domain in the charging roller having a low resistance. When the electric charges existing in the domain remain at the time of the charging step, a horizontal stripe image having a low density is generated due to over-discharge. The horizontal stripe image was evaluated as follows. The evaluation results are shown in table 5.

The image of the horizontal stripes was scanned with a scanner (trade name: image RUNNER ADVANCE C5240F, manufactured by Hewlett-Packard Company) so that the horizontal stripes thereof were directed in the horizontal direction. Thus, a photo (jpeg) data image is obtained. At this time, the scanning resolution was set to 400 × 400 dpi. The obtained photograph data Image of the horizontal stripe Image was subjected to bitmap analysis using Image analysis software (trade name: Image-Pro, Hakuto co., Ltd.). Bitmap analysis can numerically compare the shading of images. In other words, by determining a bit value difference (bit value difference) which is a difference in bit value between a horizontal stripe portion where a horizontal stripe occurs and a non-horizontal stripe portion where no horizontal stripe occurs, the degree of occurrence of a horizontal stripe can be quantitatively evaluated. The specific calculation method is as follows. The horizontal direction average bit value for each pixel in the vertical direction is determined by determining the arithmetic average of the bit values of the area where the halftone image is printed in the horizontal direction (the length direction in the charging roller) for each pixel in the vertical direction. Then, the difference between the highest horizontal direction average value of the horizontal stripe position and the horizontal direction average value of the non-horizontal stripe position is defined as a bit value difference. The bit value difference was evaluated by the following criteria.

Grade A: the bit value difference is 0.00 or more and 0.46 or less.

(the appearance of horizontal stripes could not be recognized with a magnifying glass.)

Grade B: the bit value difference is 0.47 or more and 0.83 or less.

(the appearance of horizontal stripes can be recognized with a magnifying glass, but not with the naked eye.)

Grade C: the bit value difference is 0.84 or more and 1.91 or less.

(very fine and discontinuous horizontal stripes in the longitudinal direction were recognized by the naked eye.)

Grade D: the bit value difference is 1.92 or more.

(horizontal stripes were recognized to be extremely fine and continuous in the longitudinal direction with the naked eye.)

[ examples 2 to 42]

The formulations of the unvulcanized rubber compositions according to examples 2 to 42 and the number of rotations of the blade of the pressure kneader when kneading each unvulcanized rubber composition A are shown in Table 4-1.

In addition, the extrusion conditions of the unvulcanized rubber compositions according to examples 2 to 36 and 38 to 42 are shown in Table 4-2.

In addition, the vulcanization conditions of the unvulcanized rubber rollers according to examples 2 to 42, the integrated amount of UV light used in the surface treatment of each roller or the amount of Electron Beam (EB) used in the treatment, and the presence or absence of abrasion of the outer surface of the conductive layer of each roller after vulcanization are shown in tables 4 to 3.

TABLE 4-1

TABLE 4-2

Tables 4 to 3

In the polishing according to each of examples 13 to 18, a rotary grindstone was brought into abutment with the outer surface of the conductive layer to remove a thickness of 10 μm. Thus, a crown-shaped charging roller having a diameter of 8.5mm at each of both end portions thereof in the longitudinal direction thereof and a diameter of 8.6mm at the central portion thereof was obtained. In a region from the outer surface of the conductive layer before polishing to a depth of 20 μm, there are a plurality of domains each extending so that the inferior angle θ is 90 ° or less. Therefore, by setting the polishing amount to 10 μm, the regions having the inferior angles θ of 90 ° or less can be left in the conductive layer after polishing.

In the electron beam irradiation in example 37, an electron beam irradiation apparatus (manufactured by Iwasaki Electric co., ltd.) having a maximum acceleration voltage of 150kV and a maximum current of 40mA was used, and was filled with nitrogen gas at the time of irradiation. The electron beam irradiation conditions are as follows.

Further, in example 38, press forming was performed using unvulcanized rubber composition 1 prepared in the same manner as in example 1. A combination die and a press are used in the press forming. In the split mold heated to 160 ℃, a mandrel which had been similarly heated was disposed, and an unvulcanized rubber composition was disposed along the mandrel in an amount exceeding the volume of the split mold. The weight of the unvulcanized rubber composition was prepared to be 10 g. The press forming is performed while heating a split mold in which a mandrel and an unvulcanized rubber composition are arranged. After that, burrs generated by the molding and both end portions of the vulcanized rubber layer were removed, and UV treatment was performed in the same manner as in example 1. Thus, a charging roller having an axial length of 232mm, a center outer diameter of 8.6mm and end outer diameters of 8.5mm was obtained. The molding conditions were as follows.

Pressure: 10MPa

Temperature: 160 deg.C

Time: 40 minutes

The surface resistance values of the charging rollers produced in examples 2 to 42, inferior angles formed by the line segments P and Q in the extended domains of each roller, the length of "x" of the envelope cuboid of the domains, the volume resistivity ratio m/d between the matrix and the domains of each roller, the number% of the extended domains, and the image grade and bit value differences of the rollers are shown in Table 5.

Comparative example 1

500 parts by mass of a 1% isopropyl alcohol solution of trifluoropropyltrimethoxysilane and 300 parts by mass of glass beads having an average particle diameter of 0.8mm were added to 50 parts by mass of the conductive tin oxide powder and dispersed therein with a paint shaker for 70 hours. SN-100P (manufactured by Ishihara Sangyo Kaisha, Ltd.) was used as the conductive tin oxide powder. Thereafter, the dispersion was filtered through a 500-mesh screen. Next, the solution was heated in a warm bath at 100 ℃ while stirring with a Nauta mixer. Thus, the alcohol is burned off, thereby drying the solution. After drying, a silane coupling agent is applied to the surface of the dried product to provide a surface-treated conductive tin oxide.

137 parts by mass of a polyester polyol (trade name: KYOWAPOL 1000PA, hydroxyl value: 112KOHmg, manufactured by Kyowa Hakko Kogyo co., ltd.) was dissolved in 463 parts by mass of methyl isobutyl ketone (MIBK) to provide a solution having a solid content of 16.0 mass%. 41.6 parts by mass of the above surface-treated conductive tin oxide powder and 200 parts by mass of glass beads each having a diameter of 0.8mm were added to 200 parts by mass of a polyester polyol solution, and the mixture was put into a 450 ml mayonnaise bottle and then dispersed for 6 hours with a paint shaker. Further, 330 parts by mass of the dispersion was mixed with 29.1 parts by mass of a block-type isocyanurate trimer of isophorone diisocyanate (IPDI) and 13.3 parts by mass of an isocyanurate trimer of Hexamethylene Diisocyanate (HDI). Then, the mixture was stirred with a ball mill for 1 hour. VESTANAT B1370 (manufactured by Degussa-Huls AG) was used as IPDI, and DURANATE TPA-B80E (manufactured by Asahi Kasei Corporation) was used as HDI. Finally, the solution was filtered through a 200-mesh screen so that the solid content thereof became 39.6 mass%. Thus, a coating material for a surface layer was obtained.

The above coating was applied to the surface of the vulcanized rubber roller obtained in example 1 by a dipping method.

Specifically, the coating was applied to the surface at a lifting speed of 400mm/min and air dried for 30 minutes. Thereafter, the roll axis direction was reversed, and the coating was again applied to the surface at a lifting speed of 400mm/min and then air-dried for 30 minutes. Finally, the coating was dried in an oven at 160 ℃ for 1 hour. At this time, the dried dope had a thickness of 25 μm.

Comparative example 2

A coated charging roller was obtained by the same method as in comparative example 1, except that the surface-treated conductive tin oxide was not added. At this time, the coating layer of the roller had a thickness of 26 μm.

Comparative example 3

A vulcanized rubber roller was obtained in the same manner as in example 21, except that a crown-shaped unvulcanized rubber roller having a diameter of 8.6mm at each end portion thereof and a diameter of 8.7mm at the central portion thereof was obtained by crosshead extrusion molding. The surface of the vulcanized rubber roller was ground with a rotary grindstone to a depth of 50 μm. Thus, a crown-shaped charging roller having a diameter of 8.5mm at each end portion thereof and a diameter of 8.6mm at the central portion thereof was obtained.

Comparative example 4

In addition to: the inner diameter of a die head in crosshead extrusion forming is changed to 8.6 mm; and a charging roller having a crown shape in which each end portion thereof was 8.5mm in diameter and the central portion thereof was 8.6mm in diameter was produced in the same manner as in example 1, except that the forming was performed while changing the feed speed of the mandrel.

The surface resistance values of the charging rollers produced in the above comparative examples 1 to 4, the inferior angle θ formed by the line segment P and the line segment Q in the extended domain of each roller, the length of "x" of the envelope cuboid of the domain, the volume resistivity ratio m/d between the matrix and the domain of each roller, the number% of the extended domains, and the image grade and bit value differences of the rollers are shown in table 6.

TABLE 5

TABLE 6

While the present disclosure has been described with reference to exemplary embodiments, it will be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims (7)

1. A charging roller, characterized by comprising:

a conductive mandrel; and

as a conductive layer for the surface layer,

the conductive layer includes a matrix containing a cross-linked product of a first rubber and domains dispersed in the matrix,

each of the domains contains a crosslinked material of the second rubber and conductive particles,

each of the domains has a volume resistivity smaller than that of the matrix, wherein when a cubic sample having a side of the conductive layer of 20.0 μm is sampled from an outer surface of the conductive layer to a depth of 20.0 μm, 50% or more of all the domains in the cubic sample satisfy the following condition:

conditions are as follows:

assuming that the domain to be evaluated in the cubic sample is enveloped by an enveloping cuboid having two surfaces each perpendicular to a line segment L passing through at least one arbitrary point in the domain to be evaluated and perpendicular to the surface of the mandrel,

"X" is longer than "Y" and "Z", where "X" is the length of the enveloping cuboid in the X-axis direction, "Y" is its length in the Y-axis direction, and "Z" is its length in the Z-axis direction, and

a line segment S can be drawn perpendicular to the line segment L and parallel to the X-axis.

2. The charging roller according to claim 1, wherein

When a longest line segment among line segments connecting a portion of a first YZ plane of the enveloping rectangular parallelepiped which is in contact with the domain and a portion thereof of a second YZ plane which is in contact with the domain is defined as a line segment P, and

when drawing a line segment Q having the same starting point as the starting point of the line segment P in the first or second YZ plane and perpendicular to the surface of the mandrel,

a inferior angle formed by the line segment P and the line segment Q is defined as a inferior angle θ, and a mode value of the inferior angle θ of each of all domains in the cubic sample falls within a range of 60 ° or more and 90 ° or less.

3. The charging roller according to claim 1, wherein an average value of lengths "x" of enveloping cuboids of the respective domains enveloping satisfying the condition falls within a range of 0.5 μm or more and 15.0 μm or less.

4. The charging roller according to claim 1, wherein a surface resistance value measured at an outer surface of the charging roller is 1.0 x 10^-1Omega is 1.0X 10 or more³Omega is less than or equal to.

5. The charging roller according to claim 1, wherein the volume resistivity "d" of each of the domains and the volume resistivity "m" of the matrix satisfy m/d ≧ 1.0 x 10³The relationship (2) of (c).

6. A process cartridge detachably mountable to a main body of an electrophotographic image forming apparatus, characterized by comprising:

an electrophotographic photosensitive member; and

a charging roller configured to be capable of charging the electrophotographic photosensitive member,

wherein the charging roller is the charging roller according to any one of claims 1 to 5.

7. An electrophotographic image forming apparatus, characterized by comprising:

an electrophotographic photosensitive member; and

a charging roller configured to be capable of charging the electrophotographic photosensitive member,

wherein the charging roller is the charging roller according to any one of claims 1 to 5.

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